Results and Clinical implications
We present the obstetrical outcomes of vaginal delivery after Cesarean delivery in women with and without large estimated fetal weight. Only 70.5% of women in the study group compared to 80.5% of controls experienced successful vaginal delivery (p = 0.03). This finding is in agreement with other series that examined the TOLAC’s success rate, which showed that vaginal delivery can be achieved in 60-80% of women (8, 9). However, unlike our study, those studies did not separate eLGA and non eLGA fetuses and therefore the rate of successful TOLAC in cases of eLGA fetuses cannot be elaborated.
There are several possible explanations to the difference in success rate between the two groups. One can reasonably assume, that the larger the fetus the lower the chances for successful TOLAC and the current cutoff of 4000g does not suffice. Peaceman et al. (11) reviewed the pregnancy outcomes of women whose first CD was performed because of dystocia, and found that for each 100 gram increase in birthweight relative to the first pregnancy there was 3.8% decrease in the odds of successful TOLAC. Yet, while macrosomia is considered a relative contra-indication for TOLAC, eLGA alone is not.
Women in the study group were significantly older (35 vs. 33 years; p=0.004) and, as expected, with higher gravidity (4 vs. 3; p=0.001). Nevertheless, higher gravidity is also associated with higher birthweight (12), and hence, lower rates of TOLAC. As we excluded all women who underwent more than one CD, women in the study group had more previous vaginal deliveries which should have increased their chances for a successful TOLAC (7). However, as mentioned before, we found a lower rate of successful VBAC amongst women in the study group. One reasonable explanation is that eLGA may have a greater effect on the likelihood of a successful TOLAC.
Women in the study group had higher BMI compared to the controls (30.9 vs.27.5 kg/m²; p=0.001). This finding is in accordance with the findings of Shin et al. (13) who reported that high BMI is an independent risk factor for LGA infants (13). For women attempting TOLAC, both LGA fetuses and high BMI lower the chances of TOLAC success (11, 14). It should be noted that there was no significant difference in GCT nor in gestational diabetes (GDM) between the study group and controls (p=0.97 and p=0.68 respectively). Therefore, we deduced that GCT and GDM can be ruled out as confounders to our primary outcome.
The rate of PPH was significantly increased in the study group compared to controls (7.7 vs.1.7%; p=0.001). A possible explanation for the increased rate of PPH among women in the study group could be attributed to the effect of the LGA fetus on the uterus which may cause atony. This explanation correlates with a previous study where pregnancies with LGA infants were found at higher risk for PPH (15).